The problem might be because the template files are ascii encoded and this may cause a problem when the email is set to utf-8 encoding.
To translate to Greek you should copy all of the en-US- files and rename them el-GR then translate them and if needed change the file encoding to utf-8 using your text editor.
utf-8 should work ok for Greek
You can start with translating just the files for email.
Any files that you translate you should zip them and email them to me so I can include them.
Best,
Joe